Class IndexWriter.IndexReaderWarmer

If IndexWriter.getReader() has been called (ie, this writer
is in near real-time mode), then after a merge
completes, this class can be invoked to warm the
reader on the newly merged segment, before the merge
commits. This is not required for near real-time
search, but will reduce search latency on opening a
new near real-time reader after a merge completes.

WARNING: This API is experimental and might change in incompatible ways in the next release.

NOTE: warm is called before any deletes have
been carried over to the merged segment.